This invention relates generally to stellar object sensors and, more particularly, to telescopes for use in stellar object sensors. Attitude determination and navigation in space typically rely on measurement of the angular positions of stars or solar system objects. A stellar sensor or tracker includes some form of optical telescope to focus light from a stellar object, or distant planet which presents a stellar-like appearance, onto a sensor. Preferably, a star tracker should be able to receive light from multiple fields of view simultaneously, and focus images from these fields of view onto multiple sensors located at different focal planes of the telescope. Although the primary use for devices of this type is to sense or track the positions of stellar objects, star trackers can also be used for feature recognition or scientific observation of a planetary surface, or to perform an attitude sensing function in conjunction with tracking lights on a spacecraft (a function referred to as attitude transfer), or for detecting other spacecraft in a station-keeping function in a constellation of spacecraft.
Various embodiments of a stellar sensor of the prior art are disclosed in U.S. Pat. No. 5,012,081 issued to Jungwirth et al. and U.S. Pat. No. 5,206,499 issued to Mantravadi et al. The latter patent discloses a star sensor telescope for focusing radiation from three angularly spaced fields of view onto separate sensors, using three folded Schmidt telescopes in a single enclosure. The disclosed star sensor telescope necessarily includes a holographic optical element (HOE) for spherical aberration correction, which limits the bandwidth of detectable electromagnetic radiation. There is still a need for a star sensor that is lighter in weight, smaller in size, and is of relatively low cost. The present invention fulfills this need, as will become apparent from the following summary and more detailed description.